Hydraulic booster



Patented Apr. 9, 1946 UNITED STATES PATENT OFFKIE amass nrnaauuo aoos'raa William Steiner, Detroit, Mich. Application June 11, 194:, Serial No. 490,430

11 Claims.

The invention relates to hydraulic boosters and more particularly to a hydraulic pressure booster having reciprocatory elements adapted to boost the pressure of hydraulic fluid and to transmit the latter without limitation or capacity. The invention is particularly suited for use with bydraulic brakes to increase the hydraulic pressure of the wheel cylinders in a predetermined proportion to the hydraulic pressure obtained by manual power from the master cylinder. I

Since the hydraulic displacement or diiierent braking systems varies. and is increased considerably after wear of the brake lining, it has been customary to make present-day boosters oi suirlcient capacity so as to have a certain reserve, for which reason boosters are bulky and consequently expensive. I

' It is the object or this invention to provide a booster of unlimited capacity not by increasing the size but making the operation reversible, so that at the end of a stroke the booster pistons reverse their functions and start a new stroke in the opposite direction.

Another object is to providea booster having the same function in either direction.

An important aim of the invention is to provide modulating means to control the power for the operation of the booster so that the boosted hydraulic pressure is in a predetermined proportion to the master cylinder pressure. I

Another aim is to provide a relief valve which relieves the hydraulic pressure in'the wheel cylinders quickly when the master cylinder is released. to return the fluid to the master cylinder without waiting tor the booster to attain the "oil position.

A still further aim is to provide novel and simplified means for modulating the power, making use of the reaction of the master cylinder pressure and the boosted pressure, where the piston that is responsive to the boosted pressure is acted upon on its other side by the lower, or master cylinder pressure. This feature eliminates a possible source of leakage of hydraulic iluid.

Other objects and advantages of this invention will be apparent from the following detailed description considered in connection with the accompanying drawings submitted for the purpose of illustration and not intendedto deilne the scope of the invention, reference being had for that purpose to the subjoined claims. In the drawings, wherein similar reference characters refer to similar parts:

Fig. 1 is a sectional elevation of the novel booster, connected to a hydraulic braking system which is shown diagrammatically; I

Fig. 2, a sectional elevation of the modulatin device shown in a position where power i di-' rected to the booster; and

Fig. 3, a sectional elevation of a modified form of the novel booster, also connected to a hydraulic braking system shown diagrammatically.

Before explaining the present invention in dctail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the inven tion is capable of other embodiments and of being carried out or practised in variousways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose oi'descrlption and not limitation.

Describing the invention now in detail, and referring to Fig. l, the novel booster unit is shown in combination with a conventional hydraulic braking system comprising a master cylinder l operated by the operator and wheel or slave cylinders 2 which operate the brake shoes or other device. The booster is placed intermediate the usual brake line, that leads from the master cylinder l to the wheel cylinders 2, whereby the pres sure transmitting line leading from the master cylinder to the booster is denoted by numeral 3, and iorms the primary or low pressure circuit, and l is the pressure. transmitting line leading from the booster to a plurality of wheel cylinders, forming the secondary or high pressure circuit,

The booster unit consists of housings 5 and B with a diaphragm l interposed. The latter is clamped between diaphragm plates 8 secured to a piston rod 8 carrying pistons Ill and ll provided with seals l2. These pistons slide'in axially aligned bores or cylinders I3 and I l and form cylinder chambers l5 and Hi, fluid passage to which from master cylinder 1 is provided by check valves l1 and ll; whereascheck valves l9 and 2| allow fluid to pass from chambers l5 and It, respectively, to the secondary circuit 4, but not vice versa. Guards II. merely serve as retainers for balls [1 and It,

To control the booster ratio, i. e., the proportion between the hydraulic pressure of the primary circuit and that oi the secondary circuit-v a modulating device is provided comprising a slidable piston 22 (Figure 2) with a seal 23 responsive to the hydraulic pressure of the secondary circuit to act on a lever 24 iulcrumed at 25 and opposing a slidable control piston 26 responsive to the low pressure or primary circuit.

Some of the elements are indicated by numerals in Pig. 2 only in order not to encumber the draw ings. The pressure of the secondary circuit acts on seal II and piston 22 via passage 21 and chamber ,2|, and the pressure of the primary circuit is communicated not only to piston 2| but also to the underside of piston 22 through passage 2|, cylinder chamber 80, and the bore or hole which accommodates lever 24. The latter has a forked end engaging the piston rod Ii. whose upper portion is provided with a shoulder for that purpose. A small extension of said piston rod ll pointing upwardly serves to unseat reliei ondary circuit is greater than the pre-determined multiple of the hydraulic pressure in the primary circuit. Piston 2| also serves as part of a valve valve 32 when the hydraulic pressure in the secto direct power to and from the booster and for r this purpose has a circular groove 33 in communication with the low pressure or suction line 34 connected to a source of low pressure or vacuum IS. The lower end of piston 2| also has a central bore 3| in communication with groove 3|. Bore 8| ,may be closed on by a valve discguided by its valvestem which slides in cup 4|, and urged against the housing by a spring 8| to close oi! groove 40 from pressure chamber As a source of power for the booster preferably vacuum is used, thus it illustrates the intake manifold of an internal combustion engine. whereby line 14 leads from it to groove II in valve plunger 1| adapted to slide in valve chamber I1 and provided with a seal 1| aubiected to the hydraulic pressure of the master cylinder through c 1|. A light spring I. is provided to uric the valve plunger into chamber 11. Instead of pressure line 44 of Fig. i, a pressure line H leads from chamber 4| to a source 0! air pressure H, which may be atmospheric.

Describing now the operation of the booster illustrated in Fig. i. and assuming that it is in a position as shown, depression of the foot pedal by the operator to actuate master cylinder l produces a hydraulic pressure in line 3 which is communicated to line 4 to apply the wheel cylinders 2 and thereby .actuate the brakes. The pressure 'is transmitted through check valves II, II, II and 2|,"these beingarranged to let fluid pass from 4| from which a line 42 leads to a source of fluid pressure '43. It is immaterial; as in as the principle of the invention is concerned.

whether 4| consists of atmospheric air pressure and SI of a source of vacuum, or whether I! is open to'atmospheric pressureand 43 is a source of higher fluid pressure, suchas is obtained by an air compressor.

Groove 4| is connected'withline 44' leading to chamber 45, from where-the air pressure is directed alternately through passages 48 and 4'! to one side of diaphragm I orthe other depending on the position of reversing valves 48 and 49, the

latter sliding in inserts 5|! pressed intohousings 5 and Both valves are held against each other by springs ii through the intermediary of operating levers 52 and 52' disposed in bores BI and fulcrumed at their spherical central portion 54.

The upper ends haveextending therefrom small studs or pins 65 which merely serve as a guide for springs II; It will be'noted that bores ll" are open to the low pressure or source of vacuum 35. To seal these against power chambers 5| and 51 seals or bushings 5| are provided. These may be omitted if the piston'rod 9 in size to fit cylinders l3 and i4.

Valves 4| and 49 havecircular grooves all of which are permanently in communication with passages 4| and 41, respectively, through longi-- tudinal slots 59. I

The modification shown in Fig. 3 is similar to Fig. l, with the exception that the power directed to chambers 5| or 51 is controlled by a modulating device responsive to the admitted power and the hydraulic pressure of the master cylinder and consisting of a diaphragm held by-a cover |l against housing 82, the other half of the booster housing being indicated by numeral 63 and comprising a relief valve consisting ofa ball 84 held on its seat by a lever ii'fulc'rumed at in a tapered hole, the lower end being forked to engage shoulder G! of the piston rod of piston as sliding in chamber "and subjected to the master cylinder pressure through passage HI. To allow fluid to pass from chamber II to chamber hole 6| is made somewhat larger than the diameter of lever N, or a groove 12 isprois adapted the primary circuit to the secondary circuit, but

not vice versa. The pressure is also communicated to chambers 2| and II. oi'pthemodulating valve; Because the pressure acts on both sides of piston 22, the latter has no eiiect in opposing the action oi piston 2| whereby the latter is depressed until it is in contact with disc I! and opposed by spring ll. This spring is selected to be of a definite strength to determine atwhat hydraulic pressure power-is directed to the booster. While piston-2| is pressed against disc I! passage or bore 8| is closed so'that groove 4| is shut oil from the source of; low pressure. Further depression oi the foot pedal and consequent increase in the hydraulic'pressure produced by master cylinder I causes spring 3| to yield and disc 31 to break away from groove 4|, as shown in Fig. 2,.so that air-pressure from 43 is admitted to groove 4| and from there through line .44 to chamber 4|. Valve" is shown seated and therefore does not let any, air through. However, valve 4| is open and air is able to pass via slots 5| and passage 4| into power chamber 81 to act against diaphragm 1 and to push it and piston rod 9, as well as pistons in and II towards the right to decrease the of the primary circuit.

So long as theoperator continues to. depress the brake pedal, the piston II will move to the right as viewed in Figure 4 (up to the point at which a reversal of the operation takes place as will be described) and fluid displaced from the master cylinder flows into the chamber II to fill the in creasing capacity of such chamber and to continue to exert pressure against the piston II; In order that the boosted pressure is a predetermined multiple of the primary pressure produced by the master cylinder, pistons 22 and 2| of the modulating valve as well as lever II are proportioned to eiIect the desired ratio. Thus the ratio is greater if the diameter of piston 2| is increased or that of piston 22 decreased, or if the fulcrum of lever 2! is positioned nearer to piston'v. If

the increased pressure in chamber 2| counterber 86 acting on pistons 26 and 22, spring 88 closes disc 81 to cut oil the supply of air to power chamber 51. Chamber 56 is'in'communication with the source of low pressure 85 through bore 58. Assuming now that the fluid required to fully actuate slave cylinders or wheel cylinders 2 is of such volume'that the latterare not fully actuated by one stroke of piston H, the movement of the booster pistons including diaphragm l is'reversed by the re-positioning of reversing valves 48 and 49. This is efiected by lever 52 whose forked lower end is urged to the right by piston rod 9 so that valve 49 is pushed to the left, seating valve 48 to close oil chamber 51 from the fluid pressure and to open it up to the low pressure through bore 53 at the left;' The movement of valves 48 and 49 is marked by a rapid snapping t action from one position to the other. .This is by virtue .of the fluid pressure in chamber 45 tending to keep the seated valve closed. Levers 52 and 52' are somewhat resilient whereby move ment of piston rod 9 to the right does not cause valve 49 to unseat immediately but instead flexes lever 52' slightly with an increasing force so that as soon as the seat is broken the valve snaps into the new position closing the opposite. valve 48 whose movement to seat itself on insert 56 is accelerated by the fluid pressure in chamber 45. Thus fluid pressure is admitted to chamber 56 while 51 is open to low pressure, consequently diaphragm 1, piston plates 8 and pistons l0 and II move in unison towards the left. Flor an instant during the reversal of the booster pistons all check valves are seated but as soon as the pistons move to the left valves I8 and I9 open.

At the end of the stroke piston rod 9 hits the lower forked end of lever 54 which in turn snaps valves 48 and 49 over to the right to cause reversal of the pistons in a manner similar to that described before. Thus reciprocation of the booster elements is afforded, taking place until a suflicient amount of hydraulic fluid is pumped to actuators 2 and the secondary or boosted pressure has attained a pre-determined multiple of the primary pressure. When this pressureis reached piston 22 counterbaances piston 26 whereby spring 38 seats disc 31 to close off the sup ly, of fluid pressure so that movement of pistons 18 and I! is stopped. Assuming that the operator holds the brake pedal depressed to the position correspending to the point at which the pumping action stopped, the generated braking pressure will be maintained.

Supposing now that the operator releases the brake pedal so that the pressure drops in the primary circuit, piston 22 overpowers piston 26 and raises it to first permit the disk 31 to seat and then move further upwardly until the upper extremity of piston rod 3| unseats check valve 32 allowing the secondary hydraulic pressure to relieve itself from passage 21, the fluid thus released flowing from the passage 21 into chamber 36 and to master cylinder l which returns to its "off position. At the same time, since piston 261s .in

a raised position and passage 36 open to groove Describing now the operation of the modifiedconstruction illustrated in Fig. 3, and assuming that theoperator actuates master cylinder l to produce a primary pressure in line 3, the pressure is readily transmitted through check valves 11, I8, l6, and 28 to wheel cylinders 2 which apply the brakes. The primary'hydraulic pressure also acts on piston 16 urging to compress spring 86 which has a similar function as spring 38 in Fig. 1. When the primary pressure produced by the master cylinder is sufl'icient to compress spring 86 valve plunger 16 moves to the left until groove 15 is in communication with chamber 83 and via 34 with bores 53 which become subject to lower pressure from the source of vacuum I8. Assuming valves 48 and 46 to be in a position as shown on the drawings, the air in chamber 56 becomes evacuated, while atmosphericpressure isv admitate until movement of the brake pedal is arrested. WhenJthis occurs, assuming that the motor piston is moving toward the right in Figure 3, no more fluid will be displaced from the mastercylinder but the motor piston will move toward the right a short distance, increasing the capacity of the chamber l5 and drawing fluid from the chamber 11 thereinto. motor after movement of the brake pedal is arrested will result in moving the v'alve piston 16 to a cut-oifposition and the motor will stop functioning. If the motor piston is moving in the opposite direction, fluid wil be withdrawn from the chamber 11 through lines 3, past check valve l8 into the chamber 16, and motor operation will be arrested. While modulating valve 16 is exaggerated in proportion for the purpose of illusthrough the intermediary of. lever 65.. So long as the boosted hydraulic pressure does notexceed the predetermined multiple, ball 64 remains seated, but any tendency of the boosted pressure to exceed such multiple will slightly unseat the ball 64, thus readjusting the primary and secondary pressures to the desired ratio. This ratio will be determined by the effective lever arms of the lever 65 and by the ratio of the area of the piston 68 to the efiective area of the ball 64, that is, the area corresponding to the cross-sectional area of the secondary pressure port to which the ball 64 is exposed when seated, An unseatin of the ball 64 to readjust the pressure ratio will result in a negligible now of fluid which will return to the master cylinder, or to the chamber l5 if the piston I6 should be continuing to move. As soon as the operator releases the foot pedal and the primary pressure drops the boosted Pressure acting on valve 64 ,overpowers piston 68am! un-,-,

seats ball 64 so that the fluid from the secondary circuit ma return to master cylinder I through hole 66 or groove 12.

As the primary pressure drops the suction in chamber 83 causes diaphragm 66 to push plunger 16 into cylinder 11 shuttingofl. the source of vacuum from chamber 83. However, power piston 1, 8 continues to move until the pressures in 56 and 51 are equalized, though not having any Very slight movement, of the effect on the brakes or hampering their release.

While the novel booster is illustrated in con-- junction with a conventional hydraulic braking system having a master cylinder or pressure producing means, and a plurality of wheel cylinders or pressure receiving means or actuators, I wish to make it understood that the booster disclosed may be used in many other hydraulic systems without departing from the scope of the invention. Thus pressure producing means may designate a hydraulic master cylinder ior a braking system or it ma indicate a primary source oi pressure for a function other than for applying hydraulic brakes Pressure receiving means ma indicate brake wheel cylinders or hydraulic means for actuating devices other than brakes.

As a power source for brake boosters vacuum is most commonly used because it is readily available from the intake manifold. However, the booster shown in Fig. 1' is neither dependent on this type of power alone, as 43 may represent a source of higher air pressure and 35 may be open to the atmosphere, nor does the fluid medium have to be air; instead it may represent a hydraulic pump and 35 its reservoir tank or sump.

I claim:

1. A hydraulic booster comprising a low pressure line. means for generating pressure therein, a high pressure line, a device to be operated by pressure therein, a pumping unit having a pair of chambers and a pair of devices connected together to expand one chamber while contracting the other, said chambers communicating with said high and low pressure lines, power means connected to said devices for operating them, check valves enabling fluid to flow from said low pressure lines into said chambers whereby pressure in said low pressure line assists said power means in operating said pumping unit, means for energizing said power means to generate pressure in said high pressure line when pressure in said low pressure line increases, means for reversing the action of said motor mechanism when one of said chambers has been expanded and the other contracted to a predetermined extent, and means subject to operation by pressure in said high pressure line when such pressure exceeds a predetermined multiple of the pressure in said low pressure line to relieve pressure from said high pressure line into said low pressure line,

2. A hydraulic booster comprising expansible hydraulic pressure chambers. a source of hydraulic pressure, low pressure connections from said source to said chambers, a device to be actuated by relatively high pressure, high pressure connections between said device and said chambers, check valves in said connections to permit the flow of hydraulic fluid from said low pressure connections into said chambers and from said chambers to said high pressure connections, a motor mechanism to expand and contract said chambers, means responsive to the generation of pressures in said source to energize said motor mechanism to produce pressure in said high pressure connections, a relief valve controlling communication between said high pressure connections and said low pressure connections, a control piston responsive to pressures in said low pressure connections to tend to close said relief valve, and a control piston having one end exposed to pressure in said high pressure connections to tend to open said relief valve, the latter control piston having its other end exposed to hydraulic pressure in said low pressure connections.

tioned chamber, means for reversing said motor mechanism after said piston has moved a predetermined distance, means for reversing the connections of said chambers to said lines when movement oi. 'said piston is reversed, and means for energizing said motor mechanism to generate pressure in said secondary pressure line upon a predetermined increase in pressure in said primary pressure line.

4. A hydraulic booster system comprising a primary pressure line and a secondary'pressure line, a booster intermediate said lines comprising a pair of coaxial cylinders, a pair of coaxial owosed pistons slidable in said cylinders, a motor mechanism to actuate said pistons, said lines being connected to both of said pressure chambers and being provided with check valves arranged to allow the free flow oi'tiuid from said primary line to said secondary line but to check the flow of fluid from said secondary line to said primary line, means for reversing the direction of motion of said motor mechanism when said pistons have moved in either direction to a predetermined extent, and means responsive to pressures in said primary pressure line and said secondary pressure line to establish communication between said lines when the pressure in said secondary line exceeds a predetermined multiple of the pressure in said primary line.

5. Apparatus constructed in accordance with claim 4 provided with a power-control device for said motor mechanism, and means connected to said device and responsive to pressure in said primary line and to the degree or power generated by said motor mechanism for modulating the power of said motor mechanism.

6. Apparatus constructed in accordance with claim 4 provided with a power-control'device for said motor mechanism, means responsive to pressure in said primary line and connected to said device to tend to increase the power of said motor mechanism, and means responsive to pressure in said secondary line and connected to said device to tend to decrease the power of said motor mechanism.

7. In a hydraulic braking system having a master cylinder operated b the operator and wheel cylinders to apply the brakes, a booster having hydraulic pressure chambers, fluid transmitting lines from the master cylinder to said pressure chambers and from said pressure chambers to the wheel cylinders, check valves in said pressure transmitting lines arranged to Permit the how oi hydraulic fluid from the master cylinder to said pressure chambers and from said chambers to said wheel cylinders, pistons arranged in the respective pressure chambers and movable in unison so that one piston expands its chamber while the other piston contracts its chamber, a motor mechanism to actuate said pistons, a power-control device for said motor mechanism, means for operating said device to energize said motor mechanism upon the generation of pressure in said master cylinder, means for reversing the direction of movement of said motor mechanism when said pistons have moved a predetermined distance in either direction, and means providing for the passage of fluid from said wheel cylinders to said master cylinder when the pressure in the latter is reduced.

8. A hydraulic booster comprising fluid pressure producing means, a device operable by fluid pressure, a fluid pressure transmitting means connected to said pressure producing means and to said device, a booster comprising hydraulic cylinders interposed in said pressure transmitting means, pistons slidable in the respective cylinders, power means to reciprocate said pistons in response to hydraulic pressure produced by said pressure producing means, check valves in said pressure transmitting means to prevent the flow of fluid from said cylinders to said pressure producing means and from said device to said cylinders, and means responsive to the hydraulic pressure in said device and to the hydraulic pressure in said pressure producing means to afford communication between said device and said pressure producing means when the pressure in the latter is relieved.

9. A hydraulic booster system comprising fluid pressure producing means, a device operable by fluid pressure, a hydraulic pressure booster having hydraulic cylinders and pistons slidable in the respective cylinders, fluid pressure transmitting means connecting said cylinders to said pressure producing means and to said device, check valves interposed in said pressure transmitting means to prevent the flow of fluid from said device to said cylinders and from the latter to said pressure producing means, an expansible motor mechanism to actuate said pistons, a source of fluid pressure to operate said motor mechanism, means for modulating the application of fluid pressure from said source to said motor mechanism to generate power proportionate to the pressure produced by said pressure producing means, reversing valve means to control the direction of motion of said motor mechanism, means operatively engaged with said reversing valve means and arranged to be actuated upon a predetermined movement of said pistons in either direction to reverse the operation of said motor mechanism, and means for returning fluid from said device to said pressure producing means when pressure in the latter is reduced.

10. Apparatus constructed in accordance with claim 9 wherein said reversing valve means are constructed and arranged to resist movement by said reversing means to give them a snapping action.

11. Apparatus constructed in accordance with claim 9 wh ein said reversing valve means comprises a pair of slidable valves each having a valve head urged by the pressure 01' said source, when WILLIAM STELZER. 

